This invention relates to a method and apparatus for optimized log breakdown utilizing a rotatable bandmill or scragg saw according to an optimized profile as scanned and computed.
In the prior art, logs are normally scanned and fed linearly through a double length infeed system to feed a bandmill or scragg saw for sawing into flitches and cants. The logs are scanned and rotated before they enter the double length infeed conveyor so that the logs are oriented with the horns down and or in a position to achieve maximum recovery. Once rotated, the logs enter the double length infeed conveyor one ahead of another. The logs are secured and fed towards the saws by a heavy duty lower chain and overhead press rolls within the double length infeed, where they are scanned and an optimizer/breakdown decision is made for the positioning of the chip head and saws.
In normal situations logs often are not always rotated exactly as would be optimal according to the optimizer decision. A loss of recovery results due to these small deviations in rotation. Consequently, in the prior art, a secondary scan is taken and then a minor rotation of the log is applied to correct the rotation so that a higher percentage of recovery may be achieved.
In particular, Applicant is aware of U.S. Pat. No. 5,918,653 to Knerr, which compensates for infeed rotational error by initially rescanning the log as the log passes through the double length infeed area and then attempting to compensate for any rotational error by slightly rotating the entire double length infeed in an attempt to optimize recovery.
The problem with this method is that when there are two shorter logs within the double length infeed at once, and the first log needs to be rotated, for example, 5 degrees and the second log needs to be rotated in the same direction of rotation a further 5 degrees for example and the combined 10 degrees of rotation exceeds the range of motion of the device. This results in a loss of recovery.
Thus it is an object of the present invention to improve recovery of the logs by rotating the bandmill or scragg saw, instead of the infeed, the small amount needed to correct the log orientation in order to maximize the recovery of each log.
The apparatus of the present invention is capable of correcting minor log rotational errors caused by an upstream autorotation device, by automatically rotating downstream saws as a single unit, immediately downstream of a double length infeed conveyor.
A linear scanner scans a log as the log moves linearly through the scanner on a V-flight chain. The log then moves linearly into position for autorotation in the autorotation device where the log is automatically rotated, usually so as to orient horns down as decided by an optimizer for optimized breakdown of the log using the scanner data and optimization software.
The log then moves linearly onto a stepped flight chain within the double length infeed conveyor, were the log is stablilized by over head press rolls pressing down on the stepped flight chain. The log is fed downstream along the infeed conveyor. A second scanner within the length of the double length infeed, re-scan the log for a final breakdown solution. Concurrently the optimizer also looks for higher recovery solutions at incremental angles. If a better solution at another angle is found, the saw unit , which may be dual or quad bandmills or a circular scragg saw, depending on the log size and breakdown requirements, will rotate to adjust its angular relation to the log by the optimized incremental angle as the log moves into position in front of the saw unit for sawing.
In summary, a rotatable saw unit of the present invention for optimized log breakdown of a log fed from an infeed conveyor includes a saw unit immediately downstream of an infeed conveyor and cooperating with the infeed conveyor for sawing a workpiece as the workpiece is translated by the infeed conveyor into the saw unit. The saw unit includes at least one saw aligned for sawing of the workpiece substantially parallel to a longitudinal or generally longitudinal infeed axis. An optimizing processor determines an optimized sawing orientation relative to the longitudinal infeed axis. A saw unit positioner selectively rotates the saw unit about a saw unit rotation axis so as to rotate the at least one saw into the optimized sawing orientation prior to sawing of the workpiece. The saw unit rotation axis is substantially parallel to the longitudinal infeed axis.
At least one scanner is positioned along the infeed conveyor for sensing orientation of the workpiece relative to the longitudinal infeed axis and for generating corresponding orientation data so that the optimizing processor may process the orientation data and determine the optimized sawing orientation.
The saw unit rotation axis may be adjacent the longitudinal infeed axis and may be co-axial with the longitudinal infeed axis. The at least one saw may be a band saw or a scragg saw, although this is not intended to be limiting. Alternatively, the at least one saw may be a pair of parallel bandsaws laterally spaced apart on either side of the saw unit rotation axis, and the corresponding planes are a pair of parallel planes corresponding to the pair of parallel band saws.
The saw unit may be at least one saw mounted on a corresponding at least one saw drive, wherein the at least one saw drive is mounted on a frame. Advantageously the frame is mounted on a base for selective rotational displacement relative to the base about the saw unit rotation axis by means of the saw unit positioner.
The saw unit positioner may include (a) rolling means mounted between the frame and the base, and (b) an actuator mounted to, so as to extend between, the frame and the base. The rolling means may include at least two rollers mounted in laterally spaced apart array to an underside of the frame for rolling cooperation over an arcuate track mounted on an upper surface of the base. Specifically, and without intending to be limiting, the rolling means may include first and second pairs of rollers, the first pair of rollers mounted on a first carriage pivotally mounted to a lower surface of the frame, and the second pair of rollers mounted on a second carriage pivotally mounted to the lower surface of the frame and laterally spaced apart from the first carriage, where the first and second pairs of rollers roll over and cooperate with an arcuate roller guide mounted on an upper surface of the base. The track or roller guide may be oriented laterally across the saw unit.
The invention provides other advantages which will be made clear in the description of the preferred embodiments.